Evidence for Classification

Question 1

Explain why classification systems no longer only use observable features to place organisms into groups. Give an example to support the point

Answer 1

• scientists didn’t use to always agree on the relative importance of different features and groups based solely on physical features may not show how related organisms are
• e.g Sharks and whales look quite similar and they both live in the sea, but they are not closely related. Whales are mammals and sharks are cartilaginous fish- 2 completely different classes

Question 2

What is molecular evidence and how is it used?

Answer 2

• this is looking at the similarities in proteins and DNA
• the more closely related organisms will have more similar molecules, and you can compare things like how DNA is stored and the sequence of DNA bases

Question 3

Name the other 3 ways that can help organisms be classified

Answer 3

• Embryological evidence (early stages of development)
• Anatomical evidence (structure and function)
• Behavioural evidence (behaviours and social organisation)

Question 4

Explain how new technologies (e.g new DNA techniques or better microscopes) can result in new discoveries.

Answer 4

-scientists can share their new discoveries in meetings and scientific journals, allowing for new findings to be discovered

Question 5

Explain what the new 3 domain system is and how it works.

Answer 5

• in 1990 the 3 domain system was proposed.
• these are 3 domains that are now above the 5 kingdoms in the taxonomic hierarchy
• they include Eukarya, Archaea, and Bacteria
• organisms in the prokaryotae kingdom are separated into the Archaea or Bacteria domain, whilst all other organisms with a nucleus are in the Eukarya domain, leading to 4/5 of the kingdoms

Question 6

Explain what the evidence was that led to the proposal of the 3 domain system

Answer 6

• molecular evidence was that the enzyme RNA polymerase is different in Bacteria and Archaea, and just Archaea has similar histones to Eukarya.
• therefore most scientists agreee that Archaea and Bacteria evolved separately, and that Archaea is more closely related to Eukarya then Bacteria